// SPDX-License-Identifier: MIT
// Copyright (c) 2018-2025, Advanced Micro Devices, Inc. All rights reserved.

#pragma once

#include "ck_tile/core.hpp"
#include "ck_tile/ref/conv_common.hpp"
#include <array>
#include "ck_tile/host/device_memory.hpp"
#include "ck_tile/host/kernel_launch.hpp"
#include <hip/hip_runtime.h>

namespace ck_tile {

// Naive GPU reference kernel struct for backward data grouped convolution
// Computes gradient with respect to input
// Layout: Input_grad=NDHWGC, Weight=GKZYXC, Output_grad=NDHWGK (for 3D case)
//         Input_grad=NHWGC,  Weight=GKYXC,  Output_grad=NHWGK  (for 2D case)
//         Input_grad=NWGC,   Weight=GKXC,   Output_grad=NWGK   (for 1D case)
//
// One thread per input element, uses grid-stride loop pattern

template <ck_tile::index_t NDimSpatial,
          typename InDataType,
          typename WeiDataType,
          typename OutDataType>
struct naive_grouped_conv_bwd_data_kernel
{
    static constexpr ck_tile::index_t kBlockSize = 256;

    __device__ void
    operator()(InDataType* __restrict__ p_in_grad,
               const WeiDataType* __restrict__ p_wei,
               const OutDataType* __restrict__ p_out_grad,
               // Tensor dimensions
               ck_tile::index_t G, // number of groups
               ck_tile::index_t N, // batch size
               ck_tile::index_t K, // output channels per group
               ck_tile::index_t C, // input channels per group
               // Input spatial dimensions
               const std::array<ck_tile::long_index_t, NDimSpatial>& in_spatial_lengths,
               // Weight spatial dimensions
               const std::array<ck_tile::long_index_t, NDimSpatial>& wei_spatial_lengths,
               // Output spatial dimensions
               const std::array<ck_tile::long_index_t, NDimSpatial>& out_spatial_lengths,
               // Convolution parameters
               const std::array<ck_tile::long_index_t, NDimSpatial>& conv_strides,
               const std::array<ck_tile::long_index_t, NDimSpatial>& conv_dilations,
               const std::array<ck_tile::long_index_t, NDimSpatial>& in_left_pads) const
    {
        const ck_tile::long_index_t tid         = get_block_id() * blockDim.x + get_thread_id();
        const ck_tile::long_index_t num_threads = blockDim.x * gridDim.x;

        // Calculate total input elements
        ck_tile::long_index_t input_length = G * N * C;
        for(ck_tile::index_t i = 0; i < NDimSpatial; ++i)
        {
            input_length *= in_spatial_lengths[i];
        }

        // Calculate strides for input tensor (NDHWGC or NHWGC or NWGC)
        std::array<ck_tile::long_index_t, NDimSpatial + 3> in_strides;
        ck_tile::long_index_t stride = 1;
        in_strides[NDimSpatial + 2]  = stride; // C stride
        stride *= C;
        in_strides[NDimSpatial + 1] = stride; // G stride
        stride *= G;
        for(ck_tile::index_t i = NDimSpatial - 1; i >= 0; --i)
        {
            in_strides[i + 1] = stride;
            stride *= in_spatial_lengths[i];
        }
        in_strides[0] = stride; // N stride

        // Calculate strides for output tensor (NDHWGK or NHWGK or NWGK)
        std::array<ck_tile::long_index_t, NDimSpatial + 3> out_strides;
        stride                       = 1;
        out_strides[NDimSpatial + 2] = stride; // K stride
        stride *= K;
        out_strides[NDimSpatial + 1] = stride; // G stride
        stride *= G;
        for(ck_tile::index_t i = NDimSpatial - 1; i >= 0; --i)
        {
            out_strides[i + 1] = stride;
            stride *= out_spatial_lengths[i];
        }
        out_strides[0] = stride; // N stride

        // Calculate strides for weight tensor (GKZYXC or GKYXC or GKXC)
        std::array<ck_tile::long_index_t, NDimSpatial + 3> wei_strides;
        stride                       = 1;
        wei_strides[NDimSpatial + 2] = stride; // C stride
        stride *= C;
        for(ck_tile::index_t i = NDimSpatial - 1; i >= 0; --i)
        {
            wei_strides[i + 2] = stride;
            stride *= wei_spatial_lengths[i];
        }
        wei_strides[1] = stride; // K stride
        stride *= K;
        wei_strides[0] = stride; // G stride

        // Grid-stride loop over all input elements
        for(ck_tile::long_index_t ii = tid; ii < input_length; ii += num_threads)
        {
            // Decode linear index to multi-dimensional indices
            ck_tile::long_index_t tmp = ii;

            // Extract N (batch)
            ck_tile::index_t n = tmp / in_strides[0];
            tmp -= n * in_strides[0];

            // Extract spatial dimensions
            ck_tile::index_t in_spatial_idx[6];
            for(ck_tile::index_t i = 0; i < NDimSpatial; ++i)
            {
                in_spatial_idx[i] = tmp / in_strides[i + 1];
                tmp -= in_spatial_idx[i] * in_strides[i + 1];
            }

            // Extract G (group)
            ck_tile::index_t g = tmp / in_strides[NDimSpatial + 1];
            tmp -= g * in_strides[NDimSpatial + 1];

            // Extract C (input channel)
            ck_tile::index_t c = tmp;

            // Accumulate in float
            float v_acc = 0.0f;

            // Loop over output channels
            for(ck_tile::index_t k = 0; k < K; ++k)
            {
                // Loop over filter spatial dimensions
                if constexpr(NDimSpatial == 1)
                {
                    for(ck_tile::index_t x = 0; x < wei_spatial_lengths[0]; ++x)
                    {
                        // Calculate output spatial coordinate (inverse of forward)
                        ck_tile::long_index_t w_tmp =
                            static_cast<ck_tile::long_index_t>(in_spatial_idx[0]) +
                            static_cast<ck_tile::long_index_t>(in_left_pads[0]) -
                            static_cast<ck_tile::long_index_t>(x * conv_dilations[0]);

                        // Check if this maps to valid output position
                        if(w_tmp % conv_strides[0] == 0)
                        {
                            ck_tile::long_index_t wo = w_tmp / conv_strides[0];

                            if(wo >= 0 && wo < out_spatial_lengths[0])
                            {
                                std::array<ck_tile::index_t, 1> out_spatial = {
                                    static_cast<index_t>(wo)};
                                std::array<ck_tile::index_t, 1> wei_spatial = {x};
                                ck_tile::long_index_t out_idx = detail::calculate_output_index<1>(
                                    n, g, k, out_spatial, out_strides);
                                ck_tile::long_index_t wei_idx = detail::calculate_weight_index<1>(
                                    g, k, c, wei_spatial, wei_strides);

                                v_acc += type_convert<float>(p_out_grad[out_idx]) *
                                         type_convert<float>(p_wei[wei_idx]);
                            }
                        }
                    }
                }
                else if constexpr(NDimSpatial == 2)
                {
                    for(ck_tile::index_t y = 0; y < wei_spatial_lengths[0]; ++y)
                    {
                        ck_tile::long_index_t h_tmp =
                            static_cast<ck_tile::long_index_t>(in_spatial_idx[0]) +
                            static_cast<ck_tile::long_index_t>(in_left_pads[0]) -
                            static_cast<ck_tile::long_index_t>(y * conv_dilations[0]);

                        if(h_tmp % conv_strides[0] == 0)
                        {
                            ck_tile::long_index_t ho = h_tmp / conv_strides[0];

                            if(ho >= 0 && ho < out_spatial_lengths[0])
                            {
                                for(ck_tile::index_t x = 0; x < wei_spatial_lengths[1]; ++x)
                                {
                                    ck_tile::long_index_t w_tmp =
                                        static_cast<ck_tile::long_index_t>(in_spatial_idx[1]) +
                                        static_cast<ck_tile::long_index_t>(in_left_pads[1]) -
                                        static_cast<ck_tile::long_index_t>(x * conv_dilations[1]);

                                    if(w_tmp % conv_strides[1] == 0)
                                    {
                                        ck_tile::long_index_t wo = w_tmp / conv_strides[1];

                                        if(wo >= 0 && wo < out_spatial_lengths[1])
                                        {
                                            std::array<ck_tile::index_t, 2> out_spatial = {
                                                static_cast<index_t>(ho), static_cast<index_t>(wo)};
                                            std::array<ck_tile::index_t, 2> wei_spatial = {y, x};
                                            ck_tile::long_index_t out_idx =
                                                detail::calculate_output_index<2>(
                                                    n, g, k, out_spatial, out_strides);
                                            ck_tile::long_index_t wei_idx =
                                                detail::calculate_weight_index<2>(
                                                    g, k, c, wei_spatial, wei_strides);

                                            v_acc += type_convert<float>(p_out_grad[out_idx]) *
                                                     type_convert<float>(p_wei[wei_idx]);
                                        }
                                    }
                                }
                            }
                        }
                    }
                }
                else if constexpr(NDimSpatial == 3)
                {
                    for(ck_tile::index_t z = 0; z < wei_spatial_lengths[0]; ++z)
                    {
                        ck_tile::long_index_t d_tmp =
                            static_cast<ck_tile::long_index_t>(in_spatial_idx[0]) +
                            static_cast<ck_tile::long_index_t>(in_left_pads[0]) -
                            static_cast<ck_tile::long_index_t>(z * conv_dilations[0]);

                        if(d_tmp % conv_strides[0] == 0)
                        {
                            ck_tile::long_index_t do_ = d_tmp / conv_strides[0];

                            if(do_ >= 0 && do_ < out_spatial_lengths[0])
                            {
                                for(ck_tile::index_t y = 0; y < wei_spatial_lengths[1]; ++y)
                                {
                                    ck_tile::long_index_t h_tmp =
                                        static_cast<ck_tile::long_index_t>(in_spatial_idx[1]) +
                                        static_cast<ck_tile::long_index_t>(in_left_pads[1]) -
                                        static_cast<ck_tile::long_index_t>(y * conv_dilations[1]);

                                    if(h_tmp % conv_strides[1] == 0)
                                    {
                                        ck_tile::long_index_t ho = h_tmp / conv_strides[1];

                                        if(ho >= 0 && ho < out_spatial_lengths[1])
                                        {
                                            for(ck_tile::index_t x = 0; x < wei_spatial_lengths[2];
                                                ++x)
                                            {
                                                ck_tile::long_index_t w_tmp =
                                                    static_cast<ck_tile::long_index_t>(
                                                        in_spatial_idx[2]) +
                                                    static_cast<ck_tile::long_index_t>(
                                                        in_left_pads[2]) -
                                                    static_cast<ck_tile::long_index_t>(
                                                        x * conv_dilations[2]);

                                                if(w_tmp % conv_strides[2] == 0)
                                                {
                                                    ck_tile::long_index_t wo =
                                                        w_tmp / conv_strides[2];

                                                    if(wo >= 0 && wo < out_spatial_lengths[2])
                                                    {
                                                        std::array<ck_tile::index_t, 3>
                                                            out_spatial = {
                                                                static_cast<index_t>(do_),
                                                                static_cast<index_t>(ho),
                                                                static_cast<index_t>(wo)};
                                                        std::array<ck_tile::index_t, 3>
                                                            wei_spatial = {z, y, x};
                                                        ck_tile::long_index_t out_idx =
                                                            detail::calculate_output_index<3>(
                                                                n, g, k, out_spatial, out_strides);
                                                        ck_tile::long_index_t wei_idx =
                                                            detail::calculate_weight_index<3>(
                                                                g, k, c, wei_spatial, wei_strides);

                                                        v_acc +=
                                                            type_convert<float>(
                                                                p_out_grad[out_idx]) *
                                                            type_convert<float>(p_wei[wei_idx]);
                                                    }
                                                }
                                            }
                                        }
                                    }
                                }
                            }
                        }
                    }
                }
            }

            // Convert accumulator to output type and write
            p_in_grad[ii] = type_convert<InDataType>(v_acc);
        }
    }
};

// Host-side launcher for naive grouped convolution backward data
template <ck_tile::index_t NDimSpatial,
          typename InDataType,
          typename WeiDataType,
          typename OutDataType>
CK_TILE_HOST float
naive_grouped_conv_bwd_data(InDataType* p_in_grad_dev,
                            const WeiDataType* p_wei_dev,
                            const OutDataType* p_out_grad_dev,
                            ck_tile::index_t G,
                            ck_tile::index_t N,
                            ck_tile::index_t K,
                            ck_tile::index_t C,
                            std::vector<ck_tile::long_index_t> in_spatial_lengths,
                            std::vector<ck_tile::long_index_t> wei_spatial_lengths,
                            std::vector<ck_tile::long_index_t> out_spatial_lengths,
                            std::vector<ck_tile::long_index_t> conv_strides,
                            std::vector<ck_tile::long_index_t> conv_dilations,
                            std::vector<ck_tile::long_index_t> in_left_pads,
                            ck_tile::stream_config stream_config = {})
{
    // Convert vectors to arrays
    auto in_spatial_arr     = to_array_with_default<NDimSpatial>(in_spatial_lengths);
    auto wei_spatial_arr    = to_array_with_default<NDimSpatial>(wei_spatial_lengths);
    auto out_spatial_arr    = to_array_with_default<NDimSpatial>(out_spatial_lengths);
    auto conv_strides_arr   = to_array_with_default<NDimSpatial>(conv_strides);
    auto conv_dilations_arr = to_array_with_default<NDimSpatial>(conv_dilations);
    auto in_left_pads_arr   = to_array_with_default<NDimSpatial>(in_left_pads, 0);

    // Calculate grid size
    ck_tile::long_index_t input_length = G * N * C;
    for(ck_tile::index_t i = 0; i < NDimSpatial; ++i)
    {
        input_length *= in_spatial_lengths[i];
    }

    using KernelType =
        naive_grouped_conv_bwd_data_kernel<NDimSpatial, InDataType, WeiDataType, OutDataType>;

    constexpr ck_tile::index_t block_size = KernelType::kBlockSize;
    const ck_tile::index_t grid_size      = (input_length + block_size - 1) / block_size;

    // Launch kernel
    float elapsed_ms = launch_kernel(stream_config,
                                     make_kernel(KernelType{},
                                                 dim3(grid_size),
                                                 dim3(block_size),
                                                 0, // dynamic shared memory size
                                                 p_in_grad_dev,
                                                 p_wei_dev,
                                                 p_out_grad_dev,
                                                 G,
                                                 N,
                                                 K,
                                                 C,
                                                 in_spatial_arr,
                                                 wei_spatial_arr,
                                                 out_spatial_arr,
                                                 conv_strides_arr,
                                                 conv_dilations_arr,
                                                 in_left_pads_arr));

    return elapsed_ms;
}

} // namespace ck_tile
